Isolation valve with debris control and flow tube protection

ABSTRACT

The present invention generally relates to an isolation valve with debris control. In one aspect, an isolation valve for use as part of a casing string is provided. The isolation valve includes a housing having a bore and a valve cavity. The isolation valve further includes a valve member movable between a first position in which the valve member obstructs the bore of the housing and a second position in which the valve member is disposed in the valve cavity. Further, the isolation valve includes a flow tube configured to allow movement of the valve member between the first and second positions. Additionally, the isolation valve includes an engagement assembly adapted to engage the flow tube to substantially prevent debris from entering the valve cavity when the valve member is in the second position. In another aspect, a method of operating an isolation valve in a wellbore is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention generally relate to methods and apparatusfor use in oil and gas wellbores. More particularly, the inventionrelates to an isolation valve with debris control and flow tubeprotection.

2. Description of the Related Art

An isolation valve is located as part of the casing string and operatedthrough a control line. The isolation valve is configured to temporarilyisolate a formation pressure below the isolation valve such that a toolstring may be quickly and safely tripped into a portion of the wellboreabove the isolation valve that is temporarily relieved to atmosphericpressure. Thus, the isolation valve allows the tool string to be trippedinto and out of the wellbore at a faster rate than snubbing in the toolstring under pressure. Since the pressure above the isolation valve isrelieved, the tool string can trip into the wellbore without wellborepressure acting to push the tool string out.

The isolation valve is movable between an open position and a closedposition by selectively actuating a flapper valve of the isolationvalve. The flapper valve is actuated by the movement of a flow tube inthe isolation valve. In the closed position, the flapper valve obstructsa bore through the isolation valve, and in the open position, theflapper valve resides in a flapper valve cavity. Prior designs for theisolation valve can suffer from various disadvantages. One disadvantageof prior designs is that debris and mud may enter the flapper valvecavity during operation of the isolation valve. The debris and mud mayinhibit the function of the flapper valve and thereby affect the openingand/or closing of the isolation valve. Another disadvantage of priordesigns is that an end of the flow tube oftentimes becomes damaged whilestripping or tripping the drill string through the isolation valve. Thedamaged flow tube may subsequently cause damage to the flapper valve asthe flow tube moves through the isolation valve. Therefore, there existsa need for an improved isolation valve assembly and associated methods.

SUMMARY OF THE INVENTION

The present invention generally relates to an isolation valve withdebris control. In one aspect, an isolation valve for use as part of acasing string is provided. The isolation valve includes a housing havinga bore and a valve cavity. The isolation valve further includes a valvemember movable between a first position in which the valve memberobstructs the bore of the housing and a second position in which thevalve member is disposed in the valve cavity. Further, the isolationvalve includes a flow tube configured to allow movement of the valvemember between the first and second positions. Additionally, theisolation valve includes an engagement assembly adapted to engage theflow tube to substantially prevent debris from entering the valve cavitywhen the valve member is in the second position.

In another aspect, a method of operating an isolation valve in awellbore is provided. The method includes the step of placing theisolation valve in the wellbore. The isolation valve includes a housing,a valve member, a flow tube, a piston and an engagement assembly. Themethod further includes the step of moving the valve member into a boreof the housing to obstruct a flow path through the isolation valve. Themethod also includes the step of moving the flow tube into interferencewith the valve member to open the flow path through the isolation valve.Additionally, the method includes the step of moving the flow tube intoengagement with the engagement assembly to protect the valve member fromdebris.

In yet a further aspect, an isolation valve is provided. The isolationvalve includes a housing having a bore. The isolation valve furtherincludes a flapper pivotally movable between a closed position in whichthe bore is blocked and an opened position in which the bore is open tofluid flow. The isolation valve also includes a movable flow tube forshifting the flapper between the opened position and the closedposition. Additionally, the isolation valve includes an engagementassembly adapted to engage the flow tube when the flapper is in theopened position.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

Nom FIG. 1 is a cross-section view of an isolation valve in an openposition, according to one embodiment of the invention.

FIGS. 1A and 1B are enlarged views of the isolation valve illustrated inFIG. 1.

FIG. 2 is a cross-section view of the isolation valve in a closedposition.

FIGS. 2A and 2B are enlarged views of the isolation valve illustrated inFIG. 2.

FIG. 3 is a cross-section view of the isolation valve in a lockedposition.

FIGS. 3A and 3B are enlarged views of the isolation valve illustrated inFIG. 3.

FIG. 4 is a cross-section view of an isolation valve in an openposition, according to one embodiment of the invention.

FIGS. 4A and 4B are enlarged views of the isolation valve illustrated inFIG. 4.

FIG. 5 is a cross-section view of the isolation valve in a closedposition.

FIGS. 5A and 5B are enlarged views of the isolation valve illustrated inFIG. 5.

FIG. 6 is a cross-section view of the isolation valve in a lockedposition.

FIGS. 6A and 6B are enlarged views of the isolation valve illustrated inFIG. 6.

FIGS. 7A-7C illustrate a hinge arrangement for a flapper valve.

FIG. 8 is a cross-section view of an engagement assembly.

DETAILED DESCRIPTION

Embodiments of the present invention generally relate to an isolationvalve with flow tube protection. The isolation valve may be a downholedeployment valve or a formation deployment valve. To better understandthe aspects of the present invention and the methods of use thereof,reference is hereafter made to the accompanying drawings.

FIG. 1 shows a cross-section view of an isolation valve 100 in an openposition to thereby enable tools such as a drill string to pass througha longitudinal central bore 110 of the isolation valve 100. Theisolation valve 100 includes an outer housing 115 with a flow tube 120disposed within the housing 115. The flow tube 120 represents anexemplary mechanism for moving a flapper 105 to open and close theisolation valve 100, although other types of actuators may be used insome embodiments. In one embodiment, the flapper 105 may be biased intoward the closed position and may reside in a flapper cavity 165 whenin the open position. The flow tube 120 may move within the housing 115based on control signals received to selectively displace the flapper105 between the open position and the closed position. The flow tube 120moves across an interface between the flapper 105 and a seat 130 toengage and urge the flapper 105 to the open position or disengage andallow the flapper to return to the closed position. As will be describedherein, the flow tube 120 covers the flapper 105 when the isolationvalve 100 is in the open position to at least inhibit debris anddrilling fluid from collecting around the flapper 105 and the flappercavity 165. Build-up of solids between a backside surface of the flapper105 and the housing 115 can impede the flapper 105 from moving to theclosed position after withdrawing the flow tube 120 out of interferencewith the flapper 105.

The isolation valve 100 includes control line connections 125 at an endof the housing 115 that are in communication with control lines (notshown). The control lines provide fluid via fluid channels 235, 240 tofirst and second piston chambers 135, 140 that are defined between thehousing 115 and the flow tube 120. A piston 175 spans an annular areabetween the housing 115 and the flow tube 120 to define and isolate thefirst and second chambers 135, 140 from one another. The piston 175 ismovable to change the relative sizes of the chambers 135, 140.

As shown in FIG. 1A, the piston 175 is attached to the flow tube 120 viaa releasable member 150, such as a shear pin. Fluid pressure can beintroduced into the second piston chamber 140 through the channel 240 toact on the piston 175. The fluid pressure moves the piston 175 and theattached flow tube 120 in a first direction to open the isolation valve100. In this respect, the flow tube 120 contacts the flapper 105 andurges the flapper 105 toward the flapper cavity 165. To return to theclosed position, fluid pressure is introduced in the first pistonchamber 135 via the channel 235 to act on the piston 175. The fluidpressure moves the piston 175 and the attached flow tube 120 in a secondopposite direction to slide the flow tube 120 out of interference withthe flapper 105. The isolation valve 100 may be movable between the openposition and the closed position multiple times by introducing fluidpressure in the respective piston chamber 135, 140. As also shown inFIG. 1A, a biasing member 160 is disposed between the flow tube 120 andthe piston 175. The biasing member 160 is configured to allow the flowtube 120 to move relative to the piston 175 by compressing the biasingmember 160. The biasing member 160 may be an elastomer, a spring or anyother type of biasing member known in the art. As also shown in FIG. 1A,a lock member 205 (such as a lock ring) is disposed within the housing115. The lock member 205 is compressed and held in place by a shear ring210. As will be discussed herein, the lock member 205 is configured tointeract with a groove 215 in the flow tube 120 when the isolation valve100 is moved to a locked position (FIG. 3).

As shown in FIG. 1B, the isolation valve 100 further includes anengagement assembly 170. The engagement assembly 170 is configured tointeract with the flow tube 120 when the isolation valve 100 is in theopen position in order to protect (and/or seal) the flapper cavity 165from debris. In this respect, the engagement assembly 170 may be placedbelow the flapper cavity 165. In one embodiment, the engagement assembly170 includes a guide member 180 and a sleeve member 195 that areinterconnected via a shearable member 190. The guide member 180 mayinclude a tapered inner surface that is configured to centralize a drillstring and/or other tools passing through the isolation valve 100. Inaddition, the engagement assembly 170 is configured to protect the endof the flow tube 120 from damage due to the movement of the drill stringand other tools through the isolation valve 100. In this embodiment, theengagement assembly 170 may absorb impact from the drill string becauseit is the first (or lowest) component in the isolation valve 100, whichis in contact with the drill string as the drill string moves upwardthrough the bore 110 of the isolation valve 100, the engagement assembly170 substantially shields the flow tube 120 from any damage that mayoccur. In addition, the engagement assembly may direct the drill string(using the tapered surface) into the inner diameter of the flow tube120, thereby protecting the end profile of the flow tube 120. Theengagement assembly 170 may also direct debris into the inner diameterof the flow tube 120 to prevent packing off of the flapper cavity 165.In this manner, the engagement assembly 170 may shield the flow tube 120from damage that may occur as the drill string or fluid moves upwardthrough the bore 110 of the isolation valve 100.

During opening of the isolation valve 100, the piston 175 moves the flowtube 120 in a direction toward the engagement assembly 170 when fluidpressure is introduced into the second piston chamber 140 via thechannel 240. The flow tube 120 continues in the direction until a lowerportion 155 of the flow tube 120 contacts an upper portion 185 of theguide member 180. In one embodiment, the lower portion 155 of the flowtube 120 includes a shaped surface, such as a bull-nosed shape, which isconfigured to contact with a surface on the upper portion 185 of theguide member 180. In one embodiment, the surface on the upper portion185 is shaped to mate with the shaped surface. The flow tube 120 and theguide member 180 are optionally biased against each other to maintaincontact between the flow tube 120 and the guide member 180 after theisolation valve 100 is in the open position. In the embodimentillustrated, the biasing member 160 (FIG. 1A) is used to bias the flowtube 120 against the guide member 180 of the engagement assembly 170. Inanother embodiment, a biasing member may be placed in between thecomponents of the engagement assembly 170. In further embodiment, abiasing member may be placed in the engagement assembly 170 and in theflow tube 120. The biased contact arrangement is optionally used tomaintain contact between the flow tube 120 and the guide member 180, andin this manner the flapper cavity 165 is protected from debris that mayrestrict the operation of the flapper 105.

FIG. 2 illustrates a cross-section view of the isolation valve 100 in aclosed position. As shown, the flapper 105 is obstructing thelongitudinal central bore 110 through the isolation valve 100. To closethe isolation valve 100, fluid pressure is supplied to the first pistonchamber 135 (see FIG. 2A) via the channel 235, which moves the flow tube120 out of interference with the flapper 105. Because the flapper 105 isbiased toward the seat 130, movement of the flow tube 120 out ofinterference with the flapper 105 allows the flapper 105 to move towardthe seat 130. The seat 130 is a portion of the isolation valve 100 thatengages the flapper valve 105 when the isolation valve 100 is in theclosed position. The seat 130 may be part of the housing 115, or theseat 130 may be a separate component in the isolation valve 100.Additionally, as the flow tube 120 moves through the housing 115, theflow tube 120 disengages from the guide member 180 of the engagementassembly 170 (see FIG. 2B).

FIG. 3 illustrates a cross-section view of the isolation valve 100 in alocked position. As set forth herein, the isolation valve 100 is movablebetween the open position and the closed position multiple times byintroducing fluid pressure in the respective piston chamber 135, 140.The isolation valve 100 may be locked in the open position bymanipulating the location of the flow tube 120. The flow tube 120includes inner mating profiles 145 that enable engagement of the flowtube 120 with a corresponding profile tool (not shown) for manipulatingthe location of the flow tube 120. To permit free movement of the flowtube 120 relative to the piston 175, a predetermined force is requiredto break the releasable member 150 between the flow tube 120 and thepiston 175. Upon application of the predetermined force using theprofile tool, the releasable member may break into a first portion 150Aand a second portion 150B (see FIG. 3A). Thereafter, the flow tube 120is allowed to move through the housing 115 a distance that is greaterthan a distance traveled when the isolation valve 100 is moved to theopen position. As the flow tube 120 moves through the housing 115, thegroove 215 moves to a location adjacent the lock member 205 to allow thelock member 205 to engage the groove 215. Upon engagement of the lockmember 205 in the groove 215, the flow tube 120 is locked in the openposition, and the flow tube 120 will no longer be able to move to closethe isolation valve 100. In addition, as the flow tube 120 moves throughthe housing 115, the sleeve contacts and acts on the guide member 180,which causes the shearable member 190 to shear. Thereafter, the guidemember 180 moves relative to the sleeve member 195 until the guidemember 180 contacts a shoulder 220, as shown in FIG. 3B, to accommodatethe extra travel required for the flow tube 120 during the lockingoperation.

FIG. 4 shows a cross-section view of another embodiment of an isolationvalve 300. Similar to the isolation valve 100, the isolation valve 300includes an engagement assembly 370 that is configured to interact witha flow tube 320 disposed within a housing 315. The engagement assembly370 and the flow tube 320 interact when the isolation valve 300 is inthe open position in order to protect (and/or seal) a flapper cavity 365from debris that may restrict the operation of a flapper valve 305. Theflow tube 320 is also used to allow a flapper valve 305 to open andclose the isolation valve 300.

The isolation valve 300 includes control line connections 325 that arein communication with control lines (not shown). The control linesprovide fluid to first and second piston chambers 335, 340 via fluidchannels 470, 475. The first piston chamber 335 (see FIG. 5) and thesecond piston chamber 340 (see FIG. 4) are defined between the housing315 and a piston sleeve 375. A piston sleeve 375 is movable in responseto the introduction of fluid into the piston chambers 335, 340. Thepiston sleeve 375 includes a first piston surface 435 and a secondpiston surface 440.

As shown in FIG. 4A, the piston sleeve 375 is connected to the flow tube320 via a releasable member 350. As will be described herein, thereleasable member 350 will release the connection between the pistonsleeve 375 and the flow tube 320 when the isolation valve 300 is movedto the locked position.

Referring back to FIG. 4, the isolation valve 300 is in the openposition, which allows drill string and/or other tools to pass through alongitudinal central bore 310 of the isolation valve 300. To move theisolation valve 300 to the open position, fluid pressure is introducedinto the second piston chamber 340 via the fluid channel 470. The fluidpressure in the second piston chamber 340 acts on the second pistonsurface 440 of piston sleeve 375, which moves the flow tube 320 in afirst direction to open the isolation valve 300. To return to the closedposition, fluid pressure is introduced in the first piston chamber 335via the fluid channel 475, and the fluid pressure acts on the firstpiston surface 435 of the piston sleeve 375 which moves the flow tube320 in a second opposite direction to slide the flow tube 320 out ofinterference with the flapper valve 305. In this manner, the isolationvalve 300 is movable between the open position and the closed positionmultiple times by introducing fluid pressure in the respective pistonchamber 335, 340.

As shown in FIG. 4A, a biasing member 360 is disposed between the flowtube 320 and the piston sleeve 375. The biasing member 360 is configuredto allow the flow tube 320 to move relative to the piston sleeve 375 bycompressing the biasing member 360. In one embodiment, the biasingmember 360 is a wave spring. In other embodiments, the biasing member360 may be an elastomer, a helical spring or any other type of biasingmember known in the art. As also shown in FIG. 4A, a lock member 405,such as a lock ring, is disposed within the flow tube 320. The lockmember 405 is compressed and held in place by a shear ring 410 disposedaround an outer surface of the flow tube 320. As will be discussedherein, the lock member 405 is configured to interact with a groove 415in the housing 315 when the isolation valve 300 is moved to a lockedposition.

FIG. 4B is an enlarged view of the engagement assembly 370. Theengagement assembly 370 is configured to interact with the flow tube 320when the isolation valve 300 is in the open position to substantiallyprotect a flapper cavity 365 from debris that may restrict the operationof the flapper valve 305. As shown, the engagement assembly 370 includesa guide member 380 and a sleeve member 395 that are interconnected via ashearable member 390. In one embodiment, the guide member 380 includes atapered surface that is configured to centralize a drill string and/orother tools passing through the longitudinal central bore 310 of theisolation valve 300. In addition, the engagement assembly 370 isconfigured to protect the end of the flow tube 320 from damage due tothe movement of the drill string and other tools upward through theisolation valve 300. Since the engagement assembly 370 is the first (orlowest) component in the isolation valve 300, which is in contact withthe drill string as the drill string moves upward through the bore 310of the isolation valve 300, the engagement assembly 370 substantiallyshields the flow tube 320 from any damage that may occur.

As set forth herein, the piston sleeve 375 moves the flow tube 320 in adirection toward the engagement assembly 370 when fluid pressure isintroduced into the second piston chamber 340 from the fluid channel470. The flow tube 320 moves within the housing 315 until a lowerportion 355 of the flow tube 320 is in contact with an upper portion 385of the guide member 380. In one embodiment, the lower portion 355 of theflow tube 320 includes a shaped surface, such as a bull-nosed shape,which is configured to mate with a corresponding shaped surface on theupper portion 385 of the guide member 380. The flow tube 320 and theguide member 380 are optionally biased against each other to maintaincontact between the flow tube 320 and the guide member 380 while theisolation valve 300 is in the open position. In the embodimentillustrated, the biasing member 360 (FIG. 4A) is used to bias the flowtube 320 against the guide member 380 of the engagement assembly 370. Inother embodiments, the biasing member 360 may be placed at otherlocations in the isolation valve 300, such as between the components ofthe engagement assembly 370. In another embodiment, there may be morethan one biasing member at various locations in the isolation valve 300.In this manner, the biased contact arrangement is used to maintaincontact between the flow tube 320 and the guide member 380 to protectthe flapper cavity 365 from debris that may restrict the operation ofthe flapper valve 305.

FIG. 5 illustrates a cross-section view of the isolation valve 300 in aclosed position. As shown, the flapper valve 305 is obstructing thelongitudinal central bore 310 through the isolation valve 300. To movethe isolation valve 300 to the closed position, fluid pressure issupplied to the first piston chamber 335 through the fluid channel 475,which acts on the first piston surface 435 of the piston sleeve 375 tomove the flow tube 320 out of interference with the flapper valve 305.The flapper valve 305 is biased toward the seat 330. Therefore, themovement of the flow tube 320 out of interference with the flapper valve305 allows the flapper valve 305 to move toward the seat 330. Inaddition, the movement of the flow tube 320 through the housing 315causes the flow tube 320 to disengage from the guide member 380 of theengagement assembly 370 (see FIG. 5B).

FIG. 6 illustrates a cross-section view of the isolation valve 300 in alocked position. The isolation valve 300 is movable between the openposition and the closed position multiple times by introducing fluidpressure in the respective piston chamber 335, 340. The isolation valve300 may also be locked in the open position by manipulating the locationof the flow tube 320 by mechanical force. The flow tube 320 includesinner mating profiles 345 that enable engagement of the flow tube 320with a corresponding profile tool (not shown) for manipulating thelocation of the flow tube 320. To permit free movement of the flow tube320 relative to the piston sleeve 375, a predetermined force is requiredto break the releasable member 350 between the flow tube 320 and thepiston sleeve 375. Upon application of the predetermined force, thereleasable member breaks 350 into a first portion 350A and a secondportion 350B (see FIG. 6A), which allows the flow tube 320 to moverelative to the piston sleeve 375. In addition, the application of thepredetermined force shears the ring 410. The movement of the flow tube320 through the housing 315 also moves the lock member 405 to a locationadjacent the groove 415 in the housing, and thereafter the lock member405 engages the groove 415. The flow tube 320 is locked in the openposition upon engagement of the lock member 405 in the groove 415. Atthis point, the flow tube 320 will no longer be able to move through thehousing 315 to close the isolation valve 300. As shown in FIG. 6B, themovement of the flow tube 320 through the housing causes the flow tube320 to contact and act on the guide member 380, which causes the member390 to shear. Thereafter, the guide member 380 moves relative to thesleeve member 395 to accommodate the extra travel required for the flowtube 320 during the locking operation.

FIGS. 7A-7C illustrate a hinge arrangement 425 for the flapper valve305. As shown in FIG. 7A, the hinge arrangement 425 connects the flappervalve 305 to the housing 315. During the manufacturing process of theisolation valve 300, the flapper valve 305 is aligned to allow forproper engagement of the flapper valve 305 and the seat 330. The seat330 may be part of the housing 315, or the seat 330 may a separatecomponent in the isolation valve. The design permits for small alignmentmovement along a seat/hinge mating surface 430 due to the connectionmembers. Once the hinge arrangement 425 is aligned, the hingearrangement 425 is fastened to the housing 315 by a plurality ofconnection members 420, such as screws. Further, an adjustment lockingconnection member 445 may be used to fine tune the alignment of thehinge arrangement 425 and/or to prevent axial direction movement alongthe plane of the seat/hinge mating surface 430. As shown in FIG. 7C, theadjustment locking connection member 445 is attached to a portion of thehousing 315, and the adjustment locking connection member 445 istightened in a direction along the plane of the seat/hinge matingsurface 430 and therefore prevents axial direction movement along theplane of the seat/hinge mating surface 430. Additionally, as shown inFIG. 7C, a safety connection member 495, such as a screw, snap ring orpin, is disposed at a location adjacent the adjustment lockingconnection member 445. The safety connection member 495 is configured tosubstantially prevent the adjustment locking connection member 445 frominadvertently falling out during operation of the flapper valve 305.Although the hinge arrangement 425 was described in relation to theflapper valve 305, the hinge arrangement 425 applies to other valvessuch as the flapper 105.

FIG. 8 is a cross-section view of an engagement assembly 450. Theengagement assembly 450 functions in a similar manner as describedherein with regards to the engagement assemblies 170, 370. The primarydifference is that the engagement assembly 450 is made from a singlepiece rather than two pieces (e.g., guide member and sleeve member). Theengagement assembly 450 is attached to the housing 315 via a connectionmember 460, such as a resilient connection member (e.g. o-ring) or anon-resilient connection member (e.g. shear screw). One advantage of theconnection member 460 being a resilient connection is that theconnection member 460 may be used to bias the engagement assembly 450 incontact with the flow tube 320 while the isolation valve 300 is in theopen position. The engagement assembly 450 includes a tapered surface465. The engagement assembly 450 is configured to take impact from adrill string and direct the drill string (using the tapered surface 465)into the inner diameter of the flow tube 320, thereby protecting the endprofile of the flow tube 320. The engagement assembly 450 also directsdebris into the inner diameter of the flow tube 320 to prevent packingoff of the flapper cavity 365.

Similar to as described herein, the engagement assembly 450 isconfigured to interact with the flow tube 320 when the isolation valve300 is in the open position in order to protect the flapper cavity 365from debris that may restrict the operation of a flapper valve 305. Tomaintain contact between the flow tube 320 and the engagement assembly450 while the isolation valve 300 is in the open position, one or bothof the flow tube 320 and the engagement assembly 450 are biased towardeach other. Additionally, when the isolation valve 300 is moved to thelocked position, the flow tube 320 contacts and acts on the engagementassembly 450, which causes the member 460 to shear to accommodate theextra travel required for the flow tube 320 during the lockingoperation.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. An isolation valve for use as part of a casing string, the isolationvalve comprising: a housing having a bore and a valve cavity; a valvemember movable between a first position in which the valve memberobstructs the bore of the housing and a second position in which thevalve member is disposed in the valve cavity; a flow tube configured toallow movement of the valve member between the first and secondpositions; and an engagement assembly adapted to engage the flow tube tosubstantially prevent debris from entering the valve cavity when thevalve member is in the second position.
 2. The isolation valve of claim1, further comprising a biasing member that is configured to bias theflow tube into contact with the engagement assembly when the valvemember is in the second position.
 3. The isolation valve of claim 1,wherein an end of the flow tube includes a shaped surface that isconfigured to contact a surface on the engagement assembly.
 4. Theisolation valve of claim 1, wherein the engagement assembly includes aguide member and a sleeve member interconnected via a shearable member.5. The isolation valve of claim 4, wherein the guide member includes atapered portion that is configured to centralize wellbore tools movingthrough the bore of the housing.
 6. The isolation valve of claim 1,further comprising a piston member that is connected to the flow tubevia a releasable connection.
 7. The isolation valve of claim 6, whereinthe piston member is configured to move the flow tube within the housingwhen fluid pressure acts on the piston member.
 8. The isolation valve ofclaim 6, wherein the valve member is configured to be locked in thesecond position when the connection between piston member and the flowtube is released and a connection is formed between the flow tube andthe housing.
 9. The isolation valve of claim 1, further comprising ahinge arrangement having a first portion connected to the valve memberand a second portion operatively connected to the housing.
 10. Theisolation valve of claim 9, wherein the second portion includes a hingemating surface in contact with the housing.
 11. The isolation valve ofclaim 10, wherein the hinge arrangement includes a locking connectionmember that is configured to prevent axial direction movement along aplane of the hinge mating surface during operation of the valve member.12. The isolation valve of claim 1, further comprising a resilientconnection between the engagement assembly and the housing, wherein theresilient connection is configured to bias the engagement assembly intocontact with the flow tube.
 13. The isolation valve of claim 12, whereinthe resilient connection is configured to be released when the valvemember is moved to a locked position.
 14. The isolation valve of claim1, wherein the engagement assembly is biased into contact with the flowtube.
 15. A method of operating an isolation valve in a wellbore, themethod comprising: placing the isolation valve in the wellbore, theisolation valve including a housing, a valve member, a flow tube and anengagement assembly; moving the valve member into a bore of the housingto obstruct a flow path through the isolation valve; moving the flowtube into interference with the valve member to open the flow paththrough the isolation valve; and moving the flow tube into engagementwith the engagement assembly to protect the valve member from debris.16. The method of claim 15, further comprising biasing the flow tubeagainst the engagement assembly.
 17. The method of claim 15, furthercomprising releasing a connection between the flow tube and the piston,which allows the flow tube to move independently from the piston. 18.The method of claim 17, further comprising forming a connection betweenthe flow tube and the housing to maintain the flow path through theisolation valve.
 19. An isolation valve comprising: a housing having abore; a flapper pivotally movable between a closed position in which thebore is blocked and an opened position in which the bore is open tofluid flow; a movable flow tube for shifting the flapper between theopened position and the closed position; and an engagement assemblyadapted to engage the flow tube when the flapper is in the openedposition.
 20. The isolation valve of claim 19, wherein the flow tube ismovable to a further location in the housing thereby displacing theengagement assembly and locking the flapper in the opened position.